The present invention relates generally to an improved braking system for film supply systems, and more particularly to a braking system for a film supply roll which utilizes a supply roll shaft and a generally "U" shaped shaft receiving yoke having an open top to permit ease of access for replacing an exhausted film supply roll with a fresh roll and having a friction material lining the base of the yoke to provide for controllable braking of the shaft upon interruption of operation.
In the utilization of webs of flexible films, such as in the manufacture of film products such as bags and the like, the film supply or web is normally provided in the form of a wound supply roll mounted upon an unwind stand from which the film is fed to the converting equipment. Normally, the equipment draws film to a converting station on an intermittent draw basis, and occasionally during the operation of the equipment, the converting machinery may be shut-down temporarily for one reason or another. While compensator systems employing a plurality of dancer rolls are provided for controlling the supply of film to the equipment during the normal intermittent operation of the draw rolls, means must be provided for controlling and braking the residual inertial rotational motion of the supply roll as the machine is stopped so that additional quantities of film are not uncontrollably unwound from the supply roll to thereby alter, or even eliminate any residual tension that may be present in the film web.
In the past, it has been conventional to utilize drag mechanism which make contact with the surface of the flexible film, and thus provide a restraint against continuous free-running of the film supply roll. These drag systems have normally employed canvas bags carrying a weight which frictionally engages the outer surface of the supply roll, and specifically that portion of the supply roll which comprises the film web leaving the supply roll for entry into the converting equipment. While these canvas drag systems have generally been useful for establishing web tension and, in fact, maintaining web tension, these canvas drag systems have not proven to be satisfactory for controlling the rolling of the supply roll upon interruption of machine motion. Excessive weight of the canvas drag may cause surface damage or scratching of the film. Lesser weights, on the other hand, while not adversely affecting the surface finish of the film, may not provide adequate drag forces to properly control the supply roll during shut-down. In other words, if the weight of the drag is controlled so as to not adversely affect the surface of the film web, that weight may be insufficient to properly control the free-running or rotation of the supply roll. It will be appreciated, of course, that the weight of the supply roll varies continuously as the quantities are consumed in the converting equipment, and frequently the weights available in the canvas drag systems are only sufficient to control the roll when it is partially or nearly consumed, and thus of a weight significantly less than a full roll. Normally, the weighted canvas drags provide a continuous drag on the roll so as to maintain working tension on the roll, and for ordinary systems employing the improved brake of the present invention, such canvas drags or weights will continue to be employed. Recently, however, converting equipment has been developed which runs at higher rates of speed, and with these higher speed machines, the braking torque provided by the canvas weights or drags have been found to be inadequate for shut-down. Consequently, when the operation of such a machine is interrupted, an inordinate amount of slack in the film may develop because of the inability of the canvas weights or drags to provide the necessary braking force to stop the inertial rotational motion of the supply roll.
Various braking systems have been proposed for film supply rolls which utilize brake shoes or drums which substantially entirely enclose or envelope the supply roll support shaft. While such systems are effective for applying controllable braking forces to the support shaft, these systems are undesirable from the standpoint that the braking systems must be partially disassembled in order to permit replacement of the film supply roll.